[atlas]internal timing constraints?
Daniel Karrenberg daniel.karrenberg at ripe.net
Wed Nov 24 11:26:15 CET 2010
On 24.11 10:00, Wilfried Woeber, UniVie/ACOnet wrote: > Dear Atlas folks, > > do you have a rough estimate or data about the internal timing of the > probes, like what sort of "delay" is added by the probe itself when > measuring e.g. ping RTT? > > The background is that I get different readings or ping RTTs from the > probe, compared to the "same" thing done from a regular PC running Linux > and sitting on the very same subnet, connected to the very same (small) > switch. > > The absolute difference I see is small (sub-millisecond), but it seems > to be systematic. The ping target is a "local" instance of i.root, btw. Of course there is a difference. There are many factors that contribute to that: CPU speed, protocol stack implementation, ethernet interface implementation, time keeping and measuring differences. Then thee may be different payload sizes ... And of course that is systematic. Find an example here: https://labs.ripe.net/Members/dfk/ipv6-home/ipv6-home Measuring the bsolute systematic component for the Atlas probe is on my list. However, given that it is systemactic and the absolute size is small this will not happen anytime soon. Daniel